At the 1988 Summer Olympics in

Question

Seoul, South Korea, Florence Griffith-Joyner ran the
100-meter dash in 10.49 seconds (a world record). What
was her speed in miles per hour? (1 meter is approximately
39.37 inches.)

Answer 1

1 inch = 2.54 cm exactly
So 1 mile/h
= 1760 yds * 3 ft * 12 in. * 0.0254 m / 3600 s.
= 0.44704 m/s
so
100m/10.49s
=(100/10.49)/0.44704 mph
= ? mph

Answer 2

21.32 mph